It is priorly known to manufacture cable sheaths by the steps of continuously drawing a metal strip in a longitudinal direction through a plurality of forming rollers to form a hollow tubular sheath and then continuously welding the longitudinal abutting edges of the hollow tubular member. Further, it is known to form the metal strip around a cable core prior to the step of continuously welding the longitudinal abutting edges of the sheath. Additionally, it is known to include in such cable core a plurality of electrical and/or optical conductors. As to cable sheaths for submarine cables, the aforesaid steps have generally been unsuitable in that the sheaths so formed could not withstand pressures of more than 100 BAR.
In the case of submarine cables comprising optical conductors for transoceanic transmissions, the optical conductors must be shielded from the great pressures of the deep ocean depths while bridging extensive distances. To compensate for signal attenuation along the optical conductors, amplifiers along the submarine cable are required. To energize the amplifiers, power may preferably be supplied thereto by way of the cable sheaths if they are comprised of electrical conductive metal, for example, copper or aluminum, and if their wall thicknesses are adequate to conduct the power over long distances without resulting in significant resistance heating. It is desirable to have a thick walled, cable sheath that shields the optical conductors from pressures up to 1000 BAR at deep ocean depths; while supplying power to interdispersed amplifiers without resistance heating the sheath to a level that would damage the optical conductors included therein. Further, because of the pressure load on the submarine cable at deep ocean depths, the outer diameter of the cable sheath should be kept to a minimum, especially in view of the additional requirement that the submarine cable be produced in long lengths.